The necessity of coding information prior to transmission over public channels or through public media is well known. Although the military has historically been the driving force behind the development of coding and decoding methods and apparatus, the growing use of computer networks in commercial fields, with confidential corporate data being transmitted over unsecured transmission lines, has created the need for a commercially available system which will be capable of encrypting and decrypting data at high speeds.
One commonly used method to encrypt and decrypt data is the Data Encryption Standard ("DES") announced by the Federal government in January 1977 (Federal Information Processing Standards Publication, January 16, 1977) and originally created by IBM. That algorithm for encrypting and decrypting binary information is incorporated herein
DES relies heavily on permutations of the inputted data and various "S-boxes" In DES and in this application an "S-Box" is used as an abbreviation of "Substitution Box". In such boxes, a number of preselected length is used to enter the "S-box" and a number of preselected length is outputted. Each number in a DES S-Box is carefully chosen to help randomize the data. Faster implementations of DES implement permutations by table look-ups using several bits simultaneously. In these implementations, the 32-to-32 bit permutation P which comprises an important part of the DES algorithm is effected by looking up several bits at the same time in a table. This permutation is often merged with the preceding S-box lookup. Each individual S-box in DES provides only 64 entries of 4 bits each, or 32 bytes per S-box. DES uses 8 S-boxes realized in hardware and operating in parallel to look up 8 different values simultaneously. Although this type of operation can be performed efficiently with parallel memory hardware, when and if the algorithm is "realized" in software on a conventional sequential processor, the table look-ups must occur serially, making DES exceedingly cumbersome and slow.
Another problematic aspect of DES is that the criteria used to design the S-boxes have been kept secret. Although no reason exists to believe that the S-boxes conceal a "trap door" which would enable the creators of DES to decipher DES encoded messages, it would be preferable to have a system wherein the criteria for S-box selection are made explicitly.
Finally, the size of the key used in DES has been criticized as being too small (only 56 bits) and the key schedule has been criticized for not providing adequate key mixing.
There is therefore a need for a data encryption/decryption method and apparatus which executes efficiently in software, which uses known criteria for selecting its S-boxes, and which precomputes the key.